In a continuous papermaking machine such as a Fourdrinier machine, paper sheets are formed by passing a fiber and water slurry from a headbox onto a mesh screen and draining off the water to form a sheet of paper fiber. The sheet is then moved through a press section with rollers that expresses the water, and a dryer section to reduce the moisture content from about 60% to about 5%. The dried sheet is then fed to a high-speed calendar for compaction and finishing.
The drying section is typically composed of a series of revolving suction rolls. A screen belt that supports the paper sheet passes over the suction rolls at high speed. A suction roll is generally composed of a stationary vacuum box that is centrally disposed inside a perforated cylinder or shell. The vacuum box has a slot opening and a sealing strip on either side of the opening. The sealing strips are pressed against the inner surface of the perforated shell to form a seal so that, as the perforated shell rotates about the vacuum box, water from the paper sheet is drawn through the holes of the shell and the slot opening into the vacuum box. Due to the continuous abrasive contact with the inside surface of the rotating shell, the sealing strips become worn out after a relatively short time and must be replaced, which requires a complete shutdown of the machinery.
Attempts have been made to develop sealing strips having increased durability and a longer life. U.S. Pat. No. 4,714,523 (Sawyer) discloses a sealing strip made of a wear-resistant material with a narrow inlay strip of polytetrafluoroethylene (PTFE; Teflon.TM.) that is exposed along the surface of the edge of the sealing strip. The PTFE strip rubs against the inside surface of the shell to lubricate the interface of the two elements and reduce friction. Although useful, a drawback of this sealing strip is that the PTFE insert strip can wear down to below the contact surface such that the PTFE insert is no longer effective in contacting and lubricating the shell surface. Another drawback is that the sealing strip requires an initial time interim for the PTFE to become distributed over the surface to provide a level of lubrication that allows a smooth interaction between the rotating shell and the sealing strips.
Therefore, an object of the invention is to provide a composite for forming a sealing strip for mounting in a suction roll of a papermaking machine that is highly durable and has increased compatibility and reduced abrasion against the inside surface of the perforated cylinder of a suction roll. Another object is to provide a sealing strip that will provide a high level of lubrication substantially immediately upon use and throughout the life of the sealing strip.